Positive Train Control (PTC) is a system of functional requirements for monitoring and controlling train movements for the purpose of separating trains on the same track, avoiding collisions of trains, enforcing speed requirements and speed restrictions, and protecting railroad workers, such as maintenance of way workers, bridge workers, and signal maintainers. PTC systems also monitor and control unauthorized incursions by trains, prevent train movements through switches left in the wrong position, warn of upcoming obstructions, and sometimes take control of train movements, such as bringing the train to a stop if necessary.
Prior to October 2008, PTC systems were voluntarily installed by a number of rail carriers. The Rail Safety Improvement Act of 2008 (RSIA) has mandated the widespread installation of PTC systems by the end of 2015.